What Is Hydrostatic Pressure?
Hydrostatic pressure is the pressure exerted by a fluid at rest due to the weight of the fluid above a given point. The deeper you go in a liquid, the greater the pressure, because more fluid sits above you. This principle governs everything from scuba diving and dam engineering to blood pressure and water-tower design. It is a universal physics relationship that applies anywhere there is gravity and a fluid.
How to Use This Calculator
Enter three values: the fluid density (\(\rho\)) in kilograms per cubic metre, the gravitational acceleration (\(g\)) in metres per second squared, and the depth or height (\(h\)) of the fluid column in metres. The calculator returns the pressure in pascals, with automatic conversions to kilopascals, bar, and atmospheres. Fresh water has a density of about 1000 kg/m³, seawater about 1025 kg/m³, and Earth's standard gravity is 9.81 m/s².
The Formula Explained
The governing equation is $$P = \rho \cdot g \cdot h$$ Density (\(\rho\)) tells you how much mass each cubic metre of fluid carries; gravity (\(g\)) converts that mass into weight; and depth (\(h\)) scales the result by how tall the fluid column is. The product is the gauge pressure — the pressure above atmospheric. To find absolute pressure, add atmospheric pressure (≈101,325 Pa) to the result.
Worked Example
Imagine a diver at 10 m depth in fresh water. With \(\rho = 1000\) kg/m³, \(g = 9.81\) m/s², and \(h = 10\) m: $$P = 1000 \times 9.81 \times 10 = 98{,}100 \text{ Pa}$$ which equals 98.1 kPa, 0.981 bar, or about 0.968 atm. That is nearly one extra atmosphere of pressure for every 10 metres of water — a handy rule of thumb for divers.
FAQ
Does the shape of the container matter? No. Hydrostatic pressure depends only on depth, density, and gravity — not on the container's width or volume.
Is this gauge or absolute pressure? The formula gives gauge pressure (relative to atmosphere). Add ~101,325 Pa for absolute pressure.
What value of g should I use? Use 9.81 m/s² for Earth's surface. Use a different value for other planets or precise high-altitude work.
